(1) Field of the Invention
This invention relates to an articulation joint particularly for hinge-jointed boom assemblies of the type used on construction equipment as exemplified by power cranes and shovels, for example back hoes.
(2) Description of the Prior Art
An articulation joint known in the art for such purposes comprises an articulation pin supported in a plain (sleeve) bearing. Lubrication of said known articulation joint is by hand-operated grease gun.
In boom assemblies utilizing the said articulation joint known in the art, shocks and vibrations will propagate from the equipment tool, for example the shovel a back hoe, causing severe loads and fatigue strain on vital structural components, for example hydraulic ram, sleeve bearing, articulation pin, retaining fastenings and hydraulic power unit, and at the same time subjecting the equipment operator to shocks, knocks and shudder. Hard knocks and vibrations may cause screws, bolts and hinges to work loose, thereby resulting in damage for example to inspection hatch covers, engine cover, cabin, windscreens and instrumentation. Hard knocks and vibration from the shovel may also impair the working of accumulator batteries, radiator and oil coolers.
When clearing rock using the back hoe, for example, the shovel may be directly subjected to twisting moment (torque), which by virtue of the design and construction of the known articulation joint will propagate along the tool arm, causing severe shear and point loads on the bearings, apart from anything else. Damage to the bearing surfaces may ensue.
As already noted the articulation joint known in the art is lubricated by means of a hand-operated grease gun. Knocks to the shovel may force the grease out of the sleeve bearing. Poor lubrication will aggravate wear on the sleeve bearing and articulation pin, causing play in the joint. Play allows water and dirt to enter the articulation joint, progressively increasing wear. At low temperatures the grease solidifies in the grease gun. Thawing out the gun, for example using the exhaust silencer, is arduous and time-consuming. Inadequate greasing combined with penetration of contaminants into the articulation joint lead to greater friction and may result in locking up of the articulation joint and a fractured articulation pin. Failure of the articulation pin and excessive play in the articulation joint both involve serious risk, in particular to the equipment operator.
The articulation joint of the prior art utilizes metal shims to take up lateral forces acting. These shims are subject to severe wear. They are not capable of excluding dirt and water. As the shims wear down, significant lateral play in the articulation joint ensues.